Of course, I saw that. But did you miss this part?
"The scientists in BU’s National Emerging Infectious Diseases Laboratories found that all mice infected with only the BA.1 omicron variant had mild cases and survived".
"while the combined omicron spike protein with original COVID-19 virus strain inflicted severe disease with an 80% mortality rate."
So, what they've come up with is slightly less lethal than the original virus, but orders of magnitude more lethal than the currently circulating BA.1 variant.